This invention relates to cardiac instrumentation apparatus, and more particularly to such apparatus having a pacer diagnostic capability, as for use with visual displays and the like.
The use of cardiac pacers to assist the heart in certain types of heart disease is well known. Such cardiac pacers provide an electrical stimulation pulse to the heart, hereinafter referred to generally as "pacer pulse". The pacer pulse will include a discharge pulse responsible for stimulation and may also include a recharge waveform or tail immediately following the discharge pulse. When the heart beats normally or in response to an electrical stimulation pulse, it provides an electrical waveform called an electrocardiogram pulse, hereinafter referred to as "ECG signals."
In the ECG signal of a patient equipped with a pacer, the pacer pulse usually appears prior to QRS waveforms in the overall signal. The pacer pulse may be of large or small amplitude but of very small width, typically having a duration of 1 or 2 milliseconds. It is often desirable for various monitoring and/or analytical purposes, to clearly indicate the existence and/or width of the pulse, however, because of its very small width and sometimes small amplitude, it has been difficult to repeatedly and accurately detect the present of a pacer pulse in the ECG display.
The prior art has provided several techniques for augmenting the pacer pulse as it appears in a final dislay and/or for telephonic transmission. One example is illustrated in U.S. Pat. No. 3,871,363, issued Mar. 18, 1975 for Pacer Diagnostic Instrument by Christopher C. Day. That patent describes apparatus for generating an artificial pacer pulse in response to detection of an original pacer pulse, which artificial pacer pulse is of substantially greater duration than the original pacer pulse and having a duration which may vary in proportion to the duration of the original pacer pulse. This is particularly desirable when providing for permanent recording of the ECG signal on a paper recorder.
Another example of an augmented ECG signal appears in U.S. Pat. No. 3,923,041 issued Dec. 2, 1975 for Cardiac Signal Augmentation Apparatus by Stasz et al. This patent also recognizes the desirability of providing a uniform pacer signal in response to the detection of an original pacer pulse, which uniform pacer signal is then summed with the ECG signal from which the original pacer has been removed for subsequent use, as in telephone transmission.
Further examples of circuitry for suppressing the pacer pulse (including tail) from the ECG signal and providing a uniform artificial pacer signal or tag for recombination therewith are contained in U.S. patent applications Ser. Nos. 781,816 for Pacer Tail Suppressor filed Mar. 28, 1977by Naylor et al and Ser. No. 760,487 for Artifact Suppression In Coronary Monitoring filed Jan. 19, 1977 by Marchese et al.
However, in all of the aforementioned patents, as well as all of the other prior art of which the applicant and his attorney are aware, the time-widened artificial pacer pulse is of constant polarity, regardless of the polarity of the pacer pulse which appeared in the originally detected ECG signal. In possibly the most common instance, that illustrated in the aforementioned Stasz et al patent and the Naylor et al application, an absolute value amplifier responds in the same manner to pacer pulses of either polarity to provide an artificial pacer pulse of constant polarity.
While the aforedescribed systems may be satisfactory in most instances for indicating the occurrence of pacer pulses, there are one or more situations in which it has been found desirable to also know the polarity of the sensed or detected pacer pulse. For example, some physicians while positioning the bipolar catheter tip of a pacemaker within the heart, rely upon a charge (+ to - or - to +) in the polarity of the sensed pacer pulse to provide an indication of the stability of the positioning of the catheter tip. Because of the difficulty in repeatedly and accurately perceiving the 1-2 millisecond pacer pulses appearing in the originally sensed ECG signal, it is desirable to provide artificial or standardized pacer pulses for addition to the ECG signal as previously discussed. However, there remains the problem that such standardized pacer signals will be of constant polarity regardless of the polarity of the detected pacer pulse.
Accordingly, it is a principal object of the present invention to provide improved cardiac instrumentation apparatus capable of generating standardized pacer pulse signals in response to the detection of pacer pulses and having, or at least being representative of, the polarity of the detected pacer pulses. It is a further object that such standardized pacer pulses of correct polarity be recombined with the ECG signal in appropriate time relationship such that they may be displayed and/or recorded as a single waveform.
These and other objects will be in part obvious and in part pointed out in greater detail hereinafter.